The proposed study will determine if iron therapy can correct the developmental deficits and behavioral abnormalities associated with iron deficiency anemia in infancy. The four aims of the project are: 1) to determine the level of iron depletion at which infant behavior is adversely affected, 2) to determine if there are differences between injectable and oral iron in behavioral effects, 3) to determine if iron therapy can completely correct the deficits, and 4) to confirm the specific pattern of behavioral disturbances observed in iron deficient anemic infants in our first study. The research design is a double-blind randomized controlled study of the short- and long-term behavioral and developmental effects of intramuscular and oral iron treatment. Two hundred one- to two-year old infants will be studied, 60 with iron deficiency anemia, 60 with iron deficiency with intermediate hemoglobin values, and 80 who are non-anemic, divided equally into iron depleted and iron replete groups. Their behavior and development will be assessed using sensitive quantitative behavior measures as well as overall tests of infant intelligence. To identify the level of iron depletion at which iron deficiency impairs infant development (Aim 1), pretreatment comparisons will be made in the groups of infants, whose iron status corresponds to the physiologic progression involved in becoming anemic from lack of iron. To accomplish Aim 2, the development and behavior of iron deficient infants treated with intramuscular iron will be compared to that of similar groups treated with oral iron, before treatment, after one week and after three months. Iron deficient infants will be compared with an iron replete control group before and after all babies become iron replete to determine if iron therapy can completely correct any behavioral deficits (Aim 3). Finally, (Aim 4) the study will confirm our previous results which demonstrated a specific pattern of impaired cognitive functions and a strong relationship between abnormal behavior and poor developmental test performance in iron deficient anemic infants. The results will guide practical pediatric and public health decisions about preventive strategies, screening priorities, the level of iron deficiency requiring treatment, and the mode of therapy for iron deficiency anemia, the most common nutritional disorder in the world.